For example, Japanese Patent No. 5543973 (Patent Document 1) discloses a refrigerant compressor that includes a compressing unit that compresses a refrigerant and is used in a refrigeration cycle; a vane that is slidably provided in the compressing unit and is formed of a metal material as base material; a coating film formed by sequentially stacking first to fourth layers on the surface of the base material; a roller that is rotatably provided in the compressing unit and with which a tip end of the vane is in sliding contact; and a cylinder that is provided in the compressing unit and accommodates the vane and the roller. In the refrigerant compressor, the first layer is formed of a chromium single layer, the second layer is formed of an alloy layer of chromium and tungsten carbide, the third layer is formed of an amorphous carbon layer containing metal containing at least one of tungsten and tungsten carbide, and the fourth layer is formed of an amorphous carbon layer (diamond-like carbon layer) not containing metal and containing carbon and hydrogen, and in the second layer, a content rate of chromium is higher on the first layer side than on the third layer side, and the content rate of tungsten carbide is higher on the third layer side than on the first layer side.
In addition, Japanese Laid-open Patent Publication No. 10-82390 (Patent Document 2) discloses a sliding member that includes a sliding member main body (vane) having a sliding surface; an intermediate layer provided on the sliding surface; a hard carbon coating film (diamond-like carbon coating film) provided on the intermediate layer; and a mixed layer that is formed of the components of the intermediate layer and carbon and is formed in a region inside the intermediate layer in the vicinity of the surface of the intermediate layer. In the sliding member, the mixed layer has a carbon concentration gradient such that the carbon concentration of a part close to the surface of the mixed layer is higher than that of a part separated from the surface.
However, since the vane disclosed in Patent Document 1 includes the alloy layer (second layer) and the diamond-like carbon layer (third layer) containing metal as the intermediate layers, between the chromium single layer (first layer) of the surface of the base material and the diamond-like carbon layer (fourth layer) as the sliding surface, the intermediate layers become thick, and thus the hardness difference is generated between the layers. Therefore, there is a problem in that internal residual stress is increased and the diamond-like carbon layer (fourth layer) as the sliding surface is easily peeled off.
In addition, the tungsten contained in the second and third layers is easily oxidized by acidic substances. After the oxidation, there is a problem in that the tungsten is reduced by alkaline substances so as to be easily peeled off (in the refrigerant compressor, acidic substances are present due to the deterioration of refrigerating machine oil (lubricant oil) and alkaline substances are also present due to the residue of a cleaning agent for components). Furthermore, since the number of the coating layers is as large as four, an increase in costs due to the increase in time for the film formation is also a concern.
The vane disclosed in Patent Document 2 has a problem of the adhesion (bonding properties) between the vane main body and the mixed layer as the first layer. If the vane repeatedly receives compressive stress, there is a problem in that peeling off or cracks may occur between the vane main body and the mixed layer as the first layer. In addition, in a case where tungsten, which is the constituent element of the base material of the vane is contained in the mixed layer, peeling off occurs more easily.